Remote sensing and Gis

1. Electromagnetic Radiation and Spectrum
Electromagnetic radiation is a type of energy that is all
around us and takes many forms, such as radio waves,
microwaves, X-rays and gamma-rays. Sunlight is also a
form of electromagnetic energy, but visible light is only a
small portion of the electromagnetic spectrum, which
contains a broad range of wavelengths.
In 1873, Scottish physicist James Clerk Maxwell
showed that the two phenomena were connected and
developed a unified theory of electromagnetism. The
study of electromagnetism deals with how electrically
charged particles interact with each other and with
magnetic fields.

2. In terms of the modern quantum theory,
electromagnetic radiation is the flow of photons (also
called light quanta) through space. Photons are
packets of energy that always move with the universal
speed of light.

3. Properties of EMR
Wavelength: the wavelength is the length of one
complete wave cycle which can be measured as
the distance between two successive wave
peaks.
Frequency: frequency refers to the number of
cycles of a wave passing a fixed point per unit
of time. it is generally measured in hertz(Hz).
The frequency is inversely proportional to
wavelength. Means higher wavelength lower
frequency.
Amplitude
The amplitude (a) of a wave is the distance from
the centre line (or the still position) to the top of
a crest or to the bottom of a trough.

4. Electromagnetic Waves
•Transverse waves without a medium!
•(They can travel through empty space)

7. Electromagnetic radiation spans an enormous range of wavelengths
and frequencies. This range is known as the electromagnetic
spectrum, The electromagnetic spectrum is generally divided into
seven regions, in order of decreasing wavelength and increasing
energy and frequency. The common designations are radio waves,
microwaves, infrared (IR), visible light, ultraviolet (UV) light, X-rays
and gamma-rays.
Radio waves
Radio waves are at the lowest range of the electromagnetic spectrum,
with frequencies of up to about 30 billion hertz, or 30 gigahertz (GHz),
and wavelengths greater than about 0.4 inch (10 millimeters). Radio is
used primarily for communications, including voice, data and
entertainment media.
Microwave fall in the range of the electromagnetic spectrum between
radio and IR. They have frequencies from about 3 GHz to 30 trillion
hertz, or 30 terahertz (THz), and wavelengths of about 0.004 to 0.4
inch (0.1 to 10 mm). Microwaves are used for high-bandwidth
communications and radar, as well as for a heat source for microwave
ovens and industrial applications.

8. Infrared
Infrared is in the range of the electromagnetic spectrum between
microwaves and visible light. IR has frequencies from about 30 to 400 THz
and wavelengths of about 0.00003 to 0.004 inch (740 nanometers to 100
micrometers). IR light is invisible to human eyes, but we can feel it as heat if
the intensity is sufficient.
Visible light
Visible light is found in the middle of the electromagnetic spectrum, between
IR and UV. It has frequencies of about 400 to 800 THz and wavelengths of
about 0.000015 to 0.00003 inch (380 to 740 nanometers). More generally,
visible light is defined as the wavelengths that are visible to most human
eyes.
Ultraviolet
Ultraviolet light is the range of the electromagnetic spectrum between visible
light and X-rays. It has frequencies of about 8 × 1014 to 3 x 1016 Hz and
wavelengths of about 0.0000004 to 0.000015 inch (10 to 380 nanometers).
UV light is a component of sunlight, but it is invisible to the human eye. It
has numerous medical and industrial applications, but it can damage living
tissue.

9. X-rays
X-rays are roughly classified into two types: soft X-rays and hard X-
rays. Soft X-rays make up the range of the electromagnetic spectrum
between UV and gamma-rays. Soft X-rays have frequencies of about 3
× 1016 to 1018 Hz and wavelengths of about 4 × 10−7 to 4 × 10−8 inch
(100 picometers to 10 nanometers). Hard X-rays occupy the same
region of the electromagnetic spectrum as gamma-rays. The only
difference between them is their source: X-rays are produced by
accelerating electrons, while gamma-rays are produced by atomic
nuclei.
Gamma-rays
Gamma-rays are in the range of the spectrum above soft X-rays.
Gamma-rays have frequencies greater than about 1018 Hz and
wavelengths of less than 4 × 10−9 inch (100 picometers). Gamma
radiation causes damage to living tissue, which makes it useful for
killing cancer cells when applied in carefully measured doses to small
regions. Uncontrolled exposure, though, is extremely dangerous to
humans.

11. RADIO WAVES
•Have the longest wavelengths
and lowest frequencies of all the
electromagnetic waves.

12. MICROWAVES
•Have the shortest
wavelengths and
the highest
frequency of the
radio waves.

13. VISIBLE LIGHT
•Shorter wavelength and
higher frequency than
infrared rays.
•Electromagnetic waves we
can see.
•Longest wavelength= red
light
•Shortest wavelength= violet
(purple) light

14. ULTRAVIOLET RAYS
•Shorter wavelength
and higher
frequency than
visible light
•Carry more energy
than visible light

15. X- RAYS
•Shorter wavelength
and higher
frequency than UV-
rays
•Carry a great
amount of energy
•Can penetrate most
matter.

16. GAMMA RAYS
•Shorter wavelength and
higher frequency than X-
rays
•Carry the greatest
amount of energy and
penetrate the most.